Electric switch



June 4,-1946. D. B. MacKEDRlCK y .'ZLS

ELECTRIC SWITCH Filed sept. 1o, 1945 2 sheets-sheet 1 k m E w j?? M j@ Ee 7o 7 WM WIM d l O BV.. E 69 or@ D E 5. M6 w nl m w am m 867 O wb )mii @in u l O d. 4| l n/.O l 2 4 Nw no 4 10m., 5 fo IA 2 ATTORNEY June 4, 1946., D. B. MacKENDRlcK ELECTRIC SWITCH Filed Sepf. `10,1943 2 Sheets-Sheet 2 l INVENTOR DAV/0 5. MQc//END/Q/ck BY v ,ri-J` E TTORNEY Patented June 4, 1946 UNITED STATES PATENTD OFFICE ELECTRIC SWITCH David B. MacKendrick, New YbrkgrN. Y; Application.September 10, 1943, Serial No. 501,768

This. invention relates.` to electric: switches.. More particularly itY is' directed to an electric switchwhich isvadaptedto provide-a plurality of` dierent circuit connections betweenl a supply line and an electric appliance such asA a` heating pad, percolator, toastenetc.

One object of theA invention is to provide an improved switch of. this character. which shall be of compact and rugged construction, extremely easy to assemble and manufacture and of low cost.

A further object of the invention isfto provide a switch of they character described which-will emit a sharpv and distinct click when operated` and yet comprise few and simple parts.

AA more. specic object of the invention isl toprovde an improved device of the character de scribed having an improved switching mechanism which affords a clean and positiveV contact in every position of the switch.

Other objects of the invention will in'` part be obviousv and in part hereinafter pointed outd Thev invention accordingly consists in the fea-r turesof construction, combination of elements', and arrangement of parts'which will be exemplified inthe constructionshereinafter described; and ofv whichl the'scopel of application will be indicated in the appended claims.

In the accompanyingv drawings, in which' are shown various possible embodiments of this invention and wherein like numbers referto like parts throughout,

Fig. 1 isy a topplan view of a through cord switch embodying the invention;

Figs.- 2 and 3 are enlarged longitudinal and transverse sections therethrough, taken substantially along the lines 2-2 and 3-3 respectively of'Fig. 1v;

Fig..4.is an enlarged sectionl through the rotary actuating knob taken substantially along the line 4 4 of Fig. l, the switch casing being indicated-in dot-and-dashlines;

Fig. 5V is an inside view of the two halves of the switch set side by side;

Fig. 6 is) aside elevational vie-w of the novel contact. disk Figs. 7, 8, 94 and. l0 are schematic views of the switch mechanism successively disposed to respectively connect two resistances ofv a heating appliancey in oif high, medium and low positions.;

Fig. 11 is a` longitudinal sectional view,.similar to Fig. 2, through` a switch embodying a modied form of my invention and Fig. l2 is -avview similar to Figs of saidfswitchiy ReferringY now` to the drawings and more particularly tol Figs through cord switch'V embodying the invention. Said switch may conventionally include a* casing consisting of an upper half I2 and a lower half I4 of electrically non-conductive material suitably internally recessed to receive the various operative switchv elements and eXible electric conductors. The halves" are maintained in as'- sembled relationship` by screws I5 which freely pass through smooth-bore apertures I6 in the lower half and are threaded into tapped apertures I'I in the upperhalf.

In accordanceV with the invention I associate with one of the casing halves, asrfor example'the lowery half I4, a groupof-projectons the majority of which compriseA conta-ct points to be electricallyv connected` toline and tovarious circuits of the heating appliance,r and of which at least one is-notadaptedto be so connected. These' projections, which are preferably circularly aligned and substantiallyr coplanar, are mutually separated by recessesV and are arranged to supportv a rotary disk resiliently pressed against the projec- The disk hasV av cut-out portion so located that in any: operativey position of the switch the disk will rest upon less than all of the projections.

In the switch Ill said-projections comprise four elongated electrically conductive tubular eyelets I8Y which are equiradially and equiangularly spaced around the axisof rotation of the rotary actuating knob' 20 for the switch. Each eyelet is freely received in anr aperture I9 extending through the lower casing half I 4k and has one end spun over to providel a bead 2| which sets in a countersunk recess 22' in the outer wall of saidhalf. The other ends of the' eyelet are'v likewisen spun over to form four substantially coplanar beads 24, 24', 24, 24 which are raised above the adjoining surfacey of the bottom half. Between the several heads the bottom half is cored out to provide intermediat'e'recesses 26. Ridges 28. lying between these' recesses exten radially' outward from a' hollow central hub 30 through whose tubular'wall' a slot 32 passes to connect the bore 34` of said hub to one of said recesses.y The ridges function mainly to' reinforce the hub and the walls of the apertures 2l. The level of the top surface of the hub 30 is coincident with that ofthe ridges 28, allof these parts comprisingA integral portions of the lower housing'half I4.

The ridges 28 and'recesses 26 are surrounded by anat/36 ofn appreciableareaiwhich principally 1 through 6, I0. denotes a serves as a support for means to connect three of the heads 24, 24', 24" in an electric circuit. Said means comprises a plurality of lugs 3B each having an apertured end which is placed around Ithe inside end of an eyelet before the bead 2U and head 24 are formed. The other ends of the lugs are tapped to receive binding screws 40, 4U', 40". Said screws are also threaded into tapped holes in the fiat 36. Conventional ears 42 can be employed on the tapped end of each lug to retain conductor wire around the shanks of the binding screws 40, 40', 40". Since only three lugs are provided for the four heads, one of the heads 24, hereinafter referred to as the dead or idle head, never serves to carry current from line to an electric circuit. This head, therefore, can be replaced, if desired, by a teat on the casing no higher than said head.

A jump bar 44 is secured to the lower casing half by a pair of binding screws 4E, 46', which are threaded through tapped apertures in the opposite ends of said strip and received in tapped holes in the underlying portion of the casing.

The ve binding screws 40, 40', 40, 46, 4E constitute all the means in the switch ID for connecting the circuits of an electric appliance to a source of electric current. Two of the binding screws 40, 46 adjacent one end of the casing are adapted to be connected to two flexible electric conductors 48 running to a source of electric power. The portions of these conductors within the lower casing half lie in channels 50 which converge to an exit mouth 52. The other three binding screws 40', 40", 46 at the opposite end of the casing are adapted to be connected to three flexible electric conductors 54 running to an electric appliance. The portions of these latter conductors within the lower casing half lie in channels 56 which converge to an exit mouth 58. The ribs between these last named channels 56 may be raised to ensure proper registration of the two casing halves, said ribs being adapted to be received in matching recesses 51 in the upper casing half.

It may be mentioned that the set of two bind ing screws 4U, 4B at one end of the casing are approximately equally spaced from the mouth 52 and that the binding screws at the other end of the casing are approximately equally spaced from the mouth 58. I have found that this greatly facilitates connection of conductors to the switch since the two line conductors 48 may be evenly cut off and stripped, as may the three apparatus conductors 58, there being no need to have one or more of the conductors longer or differently stripped than the others.

The flat 36 has a groove 60 formed between the widely spread portions of the line conductors 48 to receive the glass envelope of a glow lamp 62 which is enclosed in a capsule 64 of transparent material of any desired color. The capsule is held in place by a staple 64' whose legs are imbedded in the flat 36.

The heads 24, 24, 24", 24 support a rotary disk B6 of electrically conductive material. Said disk may be generally circular in outline and large enough to extend over the heads when disposed with its center coincident with the center of rotation of the actuating knob 2D. The disk has a large peripheral notch 6B of such size that when the knob 20 is in one of its four predetermined operating positions the presence of said notch will prevent the disk from contacting one of the heads. The disk will thus contact only three of said heads in any operating position of the knob. Since the disk is resiliently urged against the beads by means soon to be described, and since it only rests upon three heads at any predetermined actuating position of the switch, an even positive Contact will be maintained between the disk and any three heads in all such positions.

In switches of the character under consideration, it is desirable to have a click sound when the knob 20 moves from one predetermined operating position to another. This is accomplished in accordance with my invention by providing the disk 65 with three similarly sloped wings 10 (see Fig. 6) the tips of which have the same equiangular and equiradial spacing relative to the knob 2U as three consecutive heads 24, 24', 24". One sloping edge 'Illa of each wing is substantially coincident with the circular periphery of the disk and the other sloping edge 10b oblique or radial to said periphery so that at this latter edge 10b there is an abrupt change in height at the periphery of the disk between the tip of a wing and a flat peripheral surface lc of the disk, while at the other edge 10a the height of the periphery of the disk changes gradually. The disk is so arranged that the wings slope towards the heads 24, 24', 24, 24".

It will be appreciated that when the disk is stationary and the switch in an operating position, each wing will lie in one oi the recesses 25, while the three nat peripheral surfaces 10c rest on three of the heads 24, 2d', 24, the fourth head being registered with the notch 68 and thus out of contact with said disk.

As the disk is turned in the direction of the arrow 12 on the knob 20, each of the edges 10a will engage an underlying head and uniformly cam the disk away from the bottom casing. As rotation continues the tips of the wings will finally ride over the heads and abruptly drop into the next succeeding recesses 26 when the edges 10b clear the heads. At such time the fiat peripheral surfaces 70e will sharply strike three heads and emit a loud and distinct click. In the new position the notch 68 will be in registration 'with the next succeeding head which will thus be out of contact with said disk. The number of predetermined operative positions is determined by the number of recesses (in this case four) which are just long enough to fully receive a wing. Reverse rotation of the disk is prevented by the radia1 orientation of the edgesl 10b, and accidental forward rotation by the gradual slope of the edges 10a..

From the foregoing it will be seen that it is necessary for the means which urges the disc against the heads 24, 24', 24", 24" to be resilient, so as to allow the disk to move toward and away from said heads, and that it is desirable to provide means to mount the disk for such reciprocatory movement. To this end the upper casing half I2 may be furnished with a large central aper ture f4 through which the actuating knob 20 projects. A flange 16 around the base of the knob, which rides on an annular ridge 18 in the casing, secures the knob in position. The knob carries a central shaft 8D of non-circular crosssection, which may comprise a metal strip which is embedded in the knob and extends toward the bottom casing half i4 where it is received in the bore of the hub 30. The strip passes through an aperture 82 in the disk 55 having a contour similar to but slightly larger than the transverse profile of the shaft 8i] whereby the disk will rotate with and be slidable along the shaft.

The means forresiliently pressing thediskv against the. heads 24,141, 24v", 242'" includes a. hair, pin leaf spring |314.l one of. whose ends 8B' abuts against. the bottomfof; a well 88 in theunder surfacer of the: actuatingkn-ob; V and.l whose other end= 90 abuts against the; disk 66; Both ends-of the spring mayl bel slightly rounded asI indicated to avoid scoring.V

It is desirable to have pressure applied to the` disk in a predetermined spot relative to theY notch G8 and for this reason the spring, like. ther diski 66, is mounted for rotation. with the shaft: 86;. said shaft. passingv through. apertures S2' in. the two legs of. the spring. Theb spring' apertures. likethe. disk. aperturev 82', are oithe.- same gen,- eral. conguration a-sthe. transverse profile. of: the shaft Bil. but. large; enough". to. permit relative movement oi.y the` shaft: andspring; The spring: aperturesr 92 may be even larger thanA the disk aperture 82 since there isa tendency for said spring to bind onthe shaft because of; the relative angular movement of theY legs of the spring: and the shaft.

I prefer' to so arrangef thel spring 8.4f and diskY 66 that the end 9|)v of the spring:` presses against a spot on the. disk diametrically opposite tothe. notch 6B, since I have found that. such.: application ofi pressure insures good contact between the flat peripheral surface Ille, diametrically 0pposite to the notch, and an underlying head;

It may be pointed out that' with the construction above described assembly` ofV the switch is extremely simple since but two moving parts have to be mounted on the knob and these parts need not even be tightlyv secured thereon. The disk is prevented from accidentally falling orfV the shaft by a teat 94 near the tip of the shaft which the diskcan only passif tilted.

The outer` surface of the casing canv be.` provided with a= conventional set of identifyingnubsy 9S which enable a userto tactily ascertain the angular position of theactuating knob'.

Pursuant to an ancillary feature of thefinvention, I also provide` improvedi means f'or visually." ascertaining thel angularposition of the? actuating knob inthe dark. Such means includes an arcuate opening 98 in the upper casing half` I2 adjacent the central. aperture le, said arcuate: opening lying above the-encapsulated glow lamp' 62. Between said lamp and opening-there isv in@ terposed a transparent'. disk IIlfrnounted" forro-- tation with the knob 2B. This disk. has a' plural'- it'y of opaque 'symbols' I2 imprinted thereon and so angularly'arranged thatv the symbol appearf-- ing through the arcuate opening- 98 corresponds i to the angular position of thev knob. The glow' lamp 62 is energizedVv from the source ofzpower. One lead |04v runs from one terminal of the glow lamp to the vbinding screw through a' resistance |05. The. other terminal of the lamp is connectedby a lead |66 toa bus conductorA H382 The connection between said lead andy conductor is effected by twistingtogether said conductor and lead. The twisted portions ofthe lead and conductor are wound around Van* anchor: post'r its embedded in the lower-casing halfr Illf'and received in a .socketl III) in the upper casing half; said socket being countersunk to' receive the twisted' lead and conductor. The conductor runs from the post |08. through a passageway Si? in; the lower casing'half Iii, one ofT the recesses 26 andv the slot 32 to an eyelet I I4' restingon the bo of' the bore in the hub' 30: I' prefer to insulate substantially the. full length of the conductor |08; with a piece of tubing.t` IiIBLto prevent-'shortecircuit; Contactiis: effected between the? eyelet II,4 and' thediskf, by. a. light helical spring' I I8 seated` on the eyelet and pressing against saidv disk.. It. willbe: appreciated that whenever the disk 66 carries potential the glow lamp will be lighted',

To imparta finished appearance to the; switch andconcealzthe beads12I which anchor the eyelets I8,V I may cover the saine with a narneplate` |20 1 set. flush.- into the. outer surface of the bottom casing half and held: by drive screws |22'.

To illustrate; theY operation of my improvedk sw-itc11,in Figs..7, 8, 9 and 10 I have schematically shown` said switchA connected, byway of. example,r to a conventionalV three wirel heating pad. having.: two resistancesl |124, |26; the magnitudes of which; are. so selected. that when full line potential is applied solely to. theresistance |124 a greater'heat will. be developed than when full, line. potential is. appliedl solely to the other resistor |26.4 The various elements of the switch in said schematic; g-ures are` denoted bythe samefreference numerals asthey arein Figs. 1 through 6.

The electricv circuit from line: to the heating pad' through the switch ID'is as follows:

One linel conductor 48a is permanently connected through the binding screw 46, jump bar' 44, binding screw 46 and one apparatus con` ductor 5ta to one side of each of the two heating resistances |24, |26. TheV other side of the/first heating; resistancel |24 isV connected through an'- other apparatus conductor 5th and binding screw 5U to. thehead 24. The otherside` of the second heating resistance |25.. is connected through" the third apparatus conductor 54o and binding screw 461 t0 the headfr 215. Said rst line conductor 48u. isalsopermanently connected' through lead I iilland resistance m5' to rone terminal ofthe glow lamp 62, the other term-inal'thereof being connected through lead: |536, conductor' |08 andrhelical spring I l8r to the disk'. Theother line conductor. 48h is connected through'y binding screw 49. to. thehead 2'4" dead, that' is, it isnot adapted to be connected to line orto the heating pad.

In. Fig..7 theswitch is shown with its' elements' in off position. is-in registration with. the head 24' sothat the disk carries nopotential, both resistances |24; |26 are'unen'ergized and the glowlanip' [t2 is dark.

In 1ig..8y I. have shownl thepositionfo'f thedisk' 66 after the knobZIl has been turned approximately in the direction of the arrow '1.2; the' proper predetermined positioning ot the knob z being effected automatically by releasing the same a-ffter hearing one click. A-t this` time, the switch is in high thepadto linethat the greatest amountr of' heat will be liberated. The arrow on the knob-points to thel threeY nubsf S6 indicatethe highest heat. The-indicia |32 high appears in the arcuateopening S8.; Theorientation ofthe disk Geistes shown.. Onefat periph` eral surface'. Hic contacts the line head' 24V so' that the-diskis at the potentialofline conductor 48h. Energization of. thevdisk applies potential of. theY line tothe otherv terminal of the glow lamp 62` andf lights thesame. Another flat' peripheral surface Ilic contacts theh'ead 2li' to applyfli'ne potential through conductor 54h' toan end of the' resistance |213.. The third' llatperipheral' surface' 'idc contacts the'h'ead 2li" and appliesl line potential through appliance conductor Eile to an end of the resistance I 25. Under these conditions' both resistancesf'wil1`heat;

The. remaining? heady 2:4 is` position, that is, itso. connectsI which are recognized to The next position of the switch, assumed upon further rotation and sounding of a second click, is shown in Fig. 9. This is known as medium position. The arrow on the knob points to the two nulos recognized to indicate medium heat. The indicated medium appears through the opening 98. One iiat peripheral surface 10c contacts the line head 24". Another such surface rests on the dead head 24". The third such surface contacts the head 24 and applies the potential of line 48h to an end of the resistance |24. The head 24 connected to the resistance |26 is in registration with the notch 68 so that although line potential is applied to the glow lamp 62 and resistance |24, the resistance |26 will remain idle and heat only developed in the resistance |24.

The next partial turn of the knob 20 will place the switch in low position wherein line potential will be applied to resistance |26 but not to resistance |24. Line potential is also applied to the glow lamp.

It will be appreciated that with a switch mechanism such as described, I am able to secure excellent and even contact between the disk and heads, since in each of its four positions the disk rests against only three heads and is resiliently pressed thereagainst at a point within the triangle dened by these three heads.

In Figs. 11 and l2 I have shown a switch |30 embodying a modiiied form of my invention. The switch is generally similar to that shown in Figs. 1 through 6 in that four raised protuberances, of which three are alive and one dead, support a winged and notched disk of conductive material which is resiliently urged thereagainst. This form of switch is further similar to that previously described in that it employs a hair pin leaf spring to press the disk against the protuberances and a coil spring to maintain contact between the disk and a glow lamp as the disk shifts toward and away from said protuberances.

Said switch |30 comprises lower and upper casing halves |32, |34 which are maintained in assembled relationship by screws |36 passing through smooth-bore apertures |38 in the lower casing half and threaded into tapped apertures |40 in the upper casing half. The switch ele ments carried by the upper casing half |34 are exactly similar to the elements carried by the upper casing half I2 of the rst described form of my invention so that they will hereinafter be referred to by the same numerals and not again described.

The lower casing half |32 is recessed, except at its ends and center, to provide a large cavity |42 in the center of which is raised a tubular wall |44 having a slotted passageway |46 extending therethrough. A ledge |48 running around the periphery of the cavity receives a rectangular table |50 of insulating material which is clamped against the ledge by the upper casing half |34. The table has a central circular aperture |52 of the same size as and in registry with the bore of the tubular wall |44. The table is also provided with a plurality of arcuate apertures |54 having the same plan contour and relative posi-- tion as the recesses 26 oi the switch I0. These arcuate apertures |54 and circular aperture |52 dene a ring |56 which rests on the wall |44 and is connected to the balance of the table by four radial arms |58. Each of said arms has an aperture |60 cut therethrough to receive an eyelet 62, |62', |62, |62' whose ends are spun over to rmly secure the same to the table. One of these eyelets |62 is adapted to be connected to one of the three appliance conductors which enters the switch through a channel |64 in the lower casing half |32. The second eyelet |62' is adapted to be connected to another appliance conductor which enters the switch through a channel |66. The third appliance conductor which enters the switch through a channel |61 is adapted to be connected to an eyelet |68 extending through the table and secured thereto by spinning of its ends. The third eyelet |62 is dead, that is, it is not adapted to be connected either to line or to an appliance conductor. The fourth eyelet |62' is adapted t0 be connected to a line conductor which enters the switch through a passageway |10. The other line conductor enters the switch through passageway |12 and is adapted to be connected to an eyelet |68 extending through said table and secured thereto by spinning of its ends. The two eyelets |68, |68' are permanently electrically connected by a jump bar |14 beneath the table.

The various line and appliance conductors are connected to the eyelets |62, |62', |62", iBS, |68 by a tube |16 of malleable electrically conductive metal. To effect assembly a conductor is stripped to its cooper core strands, inserted. in a tube and the tube squeezed to flatten the same and clench it to the core. The tube may be indented during flattening to secure a rmer hold on the core. The free end of the tube is then apertured and slipped over the shank of an eyelet before the second end of the eyelet is spun.

All the eyelets are so positioned that, as with the switch I0, the line and appliance conductors can be uniformly cut and stripped.

The table is provided with an elongated slot |18 to support an encapsulated glow lamp which is fixed to the table by a metal clip |82. This glow lamp is connected in circuit as follows: lead wire |83 lies in a slot |46. One end thereof is secured to the eyelet |86 and the other end to an eyelet |84, which lies in the aperture |52. A conductor from one terminal of the lamp is wound around a split rivet |85, which is inserted in eyelet |86, and the other terminal of the lamp is Similarly wound around a split rivet inserted in eyelet |68. Connection between the eyelet |84 and the disk 66 is made by means of the coil spring |90. With a switch construction such as just described the electric parts may be assembled apart from the casing in which the table is mounted, this method of fabrication being preferred by some manufacturing concerns.

As noted above, the switch elements carried by the upper casing half |34, that is, the knob 20, shaft 80, hair pin spring 84 and disk 66, are exact ly similar to the elements denoted by the same numerals in Figs. 1 through 6, However, the upper casing half may be of slightly modied shape. For example, three ridges |88, |90 and |32 are raised on the inner surface of said casing half, the same being adapted to clamp the appliance conductor wires in the channels |64, |66 and |61. Other ridges |94, |96 clamp the line conductors in the channels |10 and |12.

The operation of the switch |30 is the same as that of the switch I0, i. e., as the knob 20 is turned, the wings 10 of the disk 66 will ride up and down over the spun heads of the eyelets |62, |62', |62, |62" facing said knob, In any one of the four operating positions, oij high medium and low, the wings will extend through the apertures |54 as indicated in Fig. 1l. at which time the three fiat peripheral surfaces 10c will press against said ends cf the eyelets and the notch `68 bridge one of the eyelets. The glow lamp will be lit whenever the appliance is connected to line in any position of the switch eX- cept oi It will thus be seen that I have provided various devices which achieve the several objects of this invention, and which are well adapted to meet the conditions of practical use.

As various possible embodiments might be made of the above invention, and as various changes might be made in the embodiments above set forth, it is t-o be understood that al1 matter herein set forth and/or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

Having thus described my invention, I claim as new and desire to secure by Letters Patent:

1. An electric switch of the character described comprising a support, a group of circularly arranged equi-angularly spaced substantially coplanar projections carried by said support, a majority of which are electrically conductive and are to be connected to line or to an electric appliance, the remainder of said projections not being adapted to be so connected, a rotary electrically conductive disk resting upon said projections, said disk being mounted to turn about an axis coincident with the center about which said projections are arranged and to move towards and away from said projections, said disk having in the periphery thereof a notch and. a plurality of wings, each of said wings having a tip, adjacent tips having the same angular spacing as said projections and being disposed the same distance from the center of rotation of the disk, each of said wings including one edge which slopes gradually from the flat periphery of the disk and another edge which provides an abrupt drop at the periphery of the disk, the peripheral flat surfaces of the disk intermediate the wings having the same angular spacing as said wings and projections and being the same distance away from the center of rotation of said disk, and means to resiliently press said disk against said projections.

2. An electric switch as set forth in claim l wherein the resilient means presses against the disk at a point disposed diametrically opposite to the notch in the periphery of the disk.

3. An electric switch as set forth in claim l wherein the resilient means comprises a spring member, one leg of which is forced against the disk at a point diametrically opposite to the notch in the periphery of the disk.

4. An electric switch as set forth in claim 1 wherein a knob is provided to turn the disk, said knob having a shaft of non-circular cross-section which is slidably received in a matching aper'ture in the disk whereby the disk is free to slide along the shaft but rotates therewith.

5. An electric switch as set forth in claim l wherein a knob is provided to turn the disk, said knob having a shaft of non-circular cross-section which is slidably received in a matching aperture in the disk and in a matching aperture in the resilient pressing means whereby said disk and resilient pressing means are free to slide relative to the shaft but will rotate therewith, said resilient pressing means pressing against a point on the disk diametrically opposite to the notch in the periphery thereof.

6. An electric switch for optionally connecting 10 an electric supply line to either one of two electric heating circuits in a three-heat electric appliance or to both of said circuits in parallel, said switch comprising a support, a group of four projections on said support equiangularly arranged about a common center, means to connect only three of said projections to line or to an appliance, said three projections, at least, being electrically conductive, an electrically conductive disk resting upon said projections, means to mount said disk in said switch for rotation about said center, means to detain said disk against accidental angular displacement in each of four quadrantallyv spaced operating positions, and means to resiliently press said disk against said projections, said disk having a cut-out portion of such size and so arranged that in any operating position of said disk, said disk rests upon only three of said projections,

7. An electric switch as set forth in claim 6 wherein the projections are circularly arranged about the axis of rotation of the disk.

8. An electric switch as set forth in claim 6 wherein the projections are substantially coplanar.

9. An electric switch as set forth in claim 6 wherein the projections are substantially coplanar and are circularly arranged about the center of rotation of the disk.

l0. An electric switch as set forth in claim 6 wherein the support for the projections is a table of insulating material, and wherein the switch includes a two-part casing between whose parts the table is clamped.

1l. An electric switch as set forth in claim 6 wherein the means to resiliently press the disk against the projections engages the disk eccentrically at a point greater than away from the cut-out portion in the disk.

l2'. An electric switch as set forth in claim 6 wherein the means for detaining the disk in its operating positions comprises three similar quad rantally spaced inclined surfaces on the disk, each surface abruptly terminating at one of its ends so that during rotation of the disk when said surfaces engage the projections the disk will be gradually forced away from said projections and when said ends of the surfaces clear the projections the disk will be suddenly forced against said projections,

13. An electric switch comprising a support, a group of projections carried by said support, a majority of which are electrically conductive and are adapted to be connected to line or to an electric appliance, a rotary electrically conductive disk resting upon said projections, means to press said disk against said projections, said disk being of such configuration that in any operating position thereof it rests upon less than all of said projections, said disk having inclined surfaces adapted to cooperate with at least three of said projections to gradually force the disk away from said projections as the disk is turned, said surfaces terminating abruptly at the periphery oi the disk, said means for pressing the disk against said projections being resilient whereby when the tips of said inclined surfaces clear said projections the intermediate peripheral portions of said disk will be suddenly forced thereagainst.

DAVID B. MACKENDRICK. 

